1. Field of the Invention
The present invention relates to an elementary stream packetizing unit for an MPEG-2 system.
2. Description of the Prior Art
An ISO (international standard organization)/IEC (international electronic commission) MPEG-2 system will be employed as an international standard. An encoder must be developed for meeting such an MPEG-2 system and for the use in a digital television (TV) broadcasting through a satellite or cable television network.
One example of MPEG-2 standard is illustrated in ISO/IEC JTC1/SC29/WG11 13818-1 Draft International Standard, Generic Coding of Moving Pictures and Associated Audio: ISO/IEC 13818-1 MPEG-2 System, November 1994. Further, MPEG-2 standard is defined as follows.
A frame consists of three rectangular matrices of integers; a luminance matrix (Y), and two chrominance matrices (Cb and Cr). A field consists of every other line of samples in the three rectangular matrices of integers representing a frame. A frame is the union of a top field and a bottom field. The top field is the field that contains the top-most line of each of the three matrices. The bottom field is the field that contains the bottom-most line of each of the three matrices.
The picture is either a frame or one field of a frame. There are three types of pictures that use different coding methods. An intra-coded picture (I picture) is coded using information only from itself. A predictive-coded picture (P picture) is a picture which is coded using motion compensated prediction from a past I picture or P picture. A bidirectionally predictive-coded picture (B picture) is a picture which is coded using motion compensated prediction from a past and/or future I picture or P picture.
The MPEG-2 system specifies a protocol for multiplexing compressed video and audio bit streams and auxiliary data. particularly, the MPEG-2 system recommends that a transport stream manner be employed in applications in which occurrence of an error in transmission is anticipated.
The transport stream manner comprises two stream layers, a packetized elementary stream (referred to hereinafter as PES) layer for packetization of the video or audio stream and a transport stream (referred to hereinafter as TS) layer for partitioning the PES in the unit of a constant size and appending a header to each partitioned stream portion to make connections to an asynchronous transfer mode (referred to hereinafter as ATM) network easy.
Each off the coded video and audio streams is packetized in the PES layer and the resultant packets are multiplexed into a single TS in the TS layer together with information necessary to demultiplexing.